Some of the more commonly used MediaWiki extensions are now included in the release tarball. These extensions are ConfirmEdit, Gadgets, Nuke, ParserFunctions, Renameuser, Vector and WikiEditor.

Gender support has been improved, meaning user pages can display the correct gender variant of "User" can now be used.

MediaWiki can now detect the camera orientation of an image from the Exif metadata, and can rotate the image thumbnail appropriately. Metadata support has been generally improved, and can now extract IPTC and XMP metadata.

Improved directionality support in 1.18 means that MediaWiki is better to use for RTL users.

The WantedPages::getSQL hook has been removed and replaced with WantedPages::getQueryInfo. This may break older extensions.

The SkinTemplateBuildContentActionUrlsAfterSpecialPage, SkinTemplateContentActions and SkinTemplateTabs hooks have been removed in favor of SkinTemplateNavigation and SkinTemplateNavigation::SpecialPage.

Skin names are no longer created based on a ucfirst version of the key in $wgValidSkinNames but now the value. This means for $wgValidSkinNames["monobook"] = "MonoBook"; the skin loader will no longer try loading SkinMonobook and will instead load SkinMonoBook.

$wgMaxUploadSize may now be set to an array to specify the upload size limit per upload type.

The options on the block form have been standardised such that checking a box makes the block 'more serious'; so while "check to prevent account creation" and "check to enable autoblock" remain the same, "check to allow user-talk edit" is reversed to "check to *disable* user-talk edit", and "check to block anon-only" becomes "check to block logged-in users too". The default settings remain the same.

Most of the field names on the Special:Block form have been changed, which will probably break screen-scraping bots.

(bug 17009) the hiddenStructure CSS class, a highly hackish way of at least *appearing* to hide article elements, has been removed. Use the ParserFunctions extension to actually remove unwanted elements from the output.

(bug 14202) $wgUseTeX has been superseded by the Math extension. To re-enable math conversion after upgrading, obtain the Math extension from SVN or from Extension:Math and add to LocalSettings.php: require_once "$IP/extensions/Math/Math.php";

$wgProfiler is now a configuration array, see StartProfiler.sample for details.

BREAKING CHANGE: Article class heirarchy split into WikiPage (backend). and Article (frontend) hierarchies. Several hooks now pass a WikiPage object instead of an Article object. These hooks all use an $article paramater as documented in hooks.txt. Extensions should be updated to account for this, though most won't require any changes.

(bug 27860) Minor edit after clicking 'new section' tab Now the "This is a minor edit" checkbox is not available when you create a page or new section.

(bug 8130) Query pages should limit to content namespaces, not just main namespace.

Search suggestions (other than in the Vector skin) will now use the HTML5 datalist feature where supported, currently only Firefox 4.

Special:Contribs now redirects to Special:Contributions.

(bug 6672) Images are now autorotated according to their EXIF orientation. This only affects thumbnails; the source remains unrotated.

(bug 29047) CSS/JS for each user group is imported from MediaWiki:Group-sysop.js, MediaWiki:Group-autoconfirmed.css, etc.

(bug 24230) Uploads of ZIP types, such as MS Office or OpenOffice can now be safely enabled. A ZIP file reader was added which can scan a ZIP file for potentially dangerous Java applets. This allows applets to be blocked specifically, rather than all ZIP files being blocked.

Added hook BitmapHandlerTransform to allow extension to transform a file without overriding the entire handler.

The parser now attempts to output markers for editsection tokens and defer the rendering of them post-cache to reduce parser cache fragmentation and ensure skin customizability of edit section links.

(bug 24755) AuthPlugin auto-creation of local accounts can now be aborted by other extensions by handling the 'AbortAutoAccount' hook, similar to the 'AbortNewAccount' triggered by explicit account creations. (They are separate to avoid loops and confusion; auth plugins like CentralAuth need to handle AbortNewAccount separately.

(bug 26033) It is now possible to count all non-redirect pages in content namespaces as articles.

Images can now be embedded in an XML dump stream using backupDump.php --include-files and can be imported using importDump.php --uploads; furthermore, it can import files from the filesystem using --image-base-path.

Three new hooks in Special:Undelete, 'UndeleteForm::showHistory', 'UndeleteForm::showRevision' and 'UndeleteForm::undelete', so that extensions may override the usage of PageArchive class and replace it with their own class that extends PageArchive.

(bug 28915) Implement QUnit test suite for MediaWiki JavaScript. Also built-in support for distribution through a TestSwarm instance.

(bug 29036) For cascade-protected pages, the mw-textarea-cprotected class is added to the textarea on the edit form.

mw.util.wikiScript has been implemented (like wfScript in GlobalFunctions.php)

(bug 29067) Expose user.tokens (like we do user.options) in ResourceLoader.

In MySQL 4.1.9+ with replication enabled, fetch the slave lag from SHOW SLAVE STATUS instead of SHOW PROCESSLIST. This ensures that lag is reported correctly in the case where there are no write events occurring. Note that the DB user now needs to have the REPLICATION CLIENT privilege if you are using replication.

Language codes in $wgDummyLanguageCodes are now excluded on localization statistics (maintenance/language/transstat.php).

(bug 29586) Make the (next 200) links on categories link directly to the relevant section of the category.

(bug 29109) Allow the automatic edit summary for redirect creation show the first bit of the new redirect page.

AjaxCategories: Easily add, edit or delete categories on article pages. Suggests possible categories when typing, all saves are done via AJAX. Supports editing of multiple categories and then saving them in one batch.

$wgAutopromoteOnce was added, allowing for users to be automatically promoted to explicit usergroups. If a group is removed from a user via Special:UserRights, it will not automatically be re-added. Configuration is similar to $wgAutopromote (see DefaultSettings.php).

The PerformRetroactiveAutoblock hook was added to allow overriding or complementing retroactive autoblock handling. This runs when blocking a user with the 'autoblock' option.

MediaWiki now supports using protocol-relative URLs in links, interwiki targets and $wgServer.

Introduced $wgVaryOnXFPForAPI which will cause the API to send Vary: X-Forwarded-Proto headers.

(bug 30722) Add an identity collation that sorts things based on what the unicode code point is (aka pre-1.17 behaviour).

(bug 30940) Add a hook in User:getDefaultOptions. To give extensions a better and more flexible way of providing default values for preferences a hook has been introdiced in User:getDefaultOptions(). Setting preferences in $wgDefaultUserOptions still work fine, but when reading them (i.e. with array_keys) to get a list of all preferences, then $wgDefaultUserOptions should no longer be used as it will contain those set via User:getDefaultOptions().

(bug 30497) Add client-nojs and client-js classes on document element to let styles easily hide or show things based on general JS availability.

(bug 31293) If Special:Userlogin is loaded over HTTPS, display MediaWiki:loginend-https instead of MediaWiki:loginend, if it's not empty. Same for signupend on the account creation page.

1.18 has several database changes since 1.17, and will not work without schema updates.

If upgrading from before 1.11, and you are using a wiki as a commons repository, make sure that it is updated as well. Otherwise, errors may arise due to database schema changes.

If upgrading from before 1.7, you may want to run refreshLinks.php to ensure new database fields are filled with data.

If you are upgrading from MediaWiki 1.4.x or earlier, some major database changes are made, and there is a slightly higher chance that things could break. Don't forget to always back up your database before upgrading!

When upgrading to 1.18.x custom skins may give errors. replace tooltipAndAccesskey with tooltipAndAccesskeyAttribs.

Documentation for both end-users and site administrators is available on MediaWiki.org, and is covered under the GNU Free Documentation License (except for pages that explicitly state that their contents are in the public domain):